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18 Tips For Modelling Structural As-Built From Laser Scan Data

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3D laser scanning has rapidly gained popularity for its automatic capture of complete as-is geometry of structures and sites.

Users have also increasingly turned to automated software tools that help them more efficiently convert rich laser scan “point clouds” into final and accurate as-built CAD and BIM deliverables.

PROJECT MANAGEMENT TIPS

  1. Establish a Data Management Plan: For large, complex projects, know beforehand (a) how you are going to process the data, (b) where the data is going to reside, (c) who is going to have authorized access to the data, and (d) how all data will be tied together to complete the project.
  2. Use One Team for Scanning AND Modeling: When possible, use the same field staff to also process scan and photogrammetric data in the office. They will be more familiar with the project, which leads to higher office efficiency and reduces the risk of getting something wrong or missing something.
  3. Understand the Use Case: Make sure you understand exactly what the as-builts will be used for. Is it for general planning purposes? Is it for exact structural and/or clash analysis? Do the drawings need to show everything square and plumb or do they need to show deflection and out-of-plum situations? The answers can have a significant impact on the level of accuracy needed and on modeling time and methodology.

FIELD DATA CAPTURE TIPS

  1. Use Multiple Scanners for Maximum Efficiency: Using two scanners and two field staff for one day is more efficient than using one scanner with one person for two (2) days.
  2. Spheres and Targets are your Friend: Using spheres/scan targets for registration enables valuable checking and QC. 
  3. Control Prevents Chaos! Tying into survey control is good practice, when feasible (with a nod to Maxwell Smart).
  4. Scan Density Matters: Scanning at higher density, higher accuracy, and lower scan noise settings makes modeling easier in the office; likewise, scanning from more perspectives – even if it’s done at lower data quality settings with noisier scan data – also makes modeling easier in the office, as it captures more sides of objects.
  5. Add a Drone to your Reality Capture Quiver: Photogrammetric drones can be a viable option for capturing roof or other geometry that may be difficult or unsafe to access with a laser scanner. Overlapping drone images can be stitched together and converted to point clouds and then combined with interior building scans.

 

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OFFICE (MODELING & DELIVERABLE CREATION) TIPS

  1. Older Structure is Often Atypical: Don’t assume that all structural bays are “typical”. Especially for older buildings, individual elements may have been beefed up or modified; truss systems may have been designed and built differently. Scan and model elements - don’t rely on the naked eye!
  2. Make Trusses a Family Affair: Create In-Place Truss Families in Revit and convert them to Loadable Families.
  3. EdgeWise Ground Extraction Gives Important Context: Auto-extracting ground in EdgeWise (via LandXML and Revit’s Site Designer tool) is valuable for keeping the building model in context of the surrounding outside landscape and hardscape, should modifications be considered for those areas.
  4. Use QA Tools to Spot and Correct False Positives: Laser scanning captures everything that a scanner can reach and detect a laser return. As a result, auto-extraction of point cloud data can periodically create “false positives”, i.e. something is extracted from scan points that’s not really a true pipe, duct, etc. However, EdgeWise has powerful QC/QA tools that aid in efficiently sorting these out.
  5. Use Verity as a Model Checker: Although Verity software is primarily intended for construction QA, it can also be used to validate the quality of the as-built model and to make sure it accurately conforms to the point cloud. This is particularly valuable as a QA check on inexperienced modelers or outsourced modeling jobs. In addition, Verity can provide better quantitative understanding of real world variances, such as beam deflection.
  6. EdgeWise for Repetitive Elements, Revit for One-Offs: To best handle out-of-plane walls, use EdgeWise auto-extraction tools for repetitive applications; for one-off applications, manual tools in AutoCAD or Revit may be sufficient. It’s possible to create “heat map” type deliverables that show variations in wall surface flatness; however, be careful about “over specifying” accuracy of modeled walls, as construction tolerances, for example for dry wall surfaces, are bigger than typical modeling specs.
  7. Don’t Forget to Add Non-Standard Specs: Although EdgeWise extracts to industry standard steel and piping geometries from a comprehensive database, non-standard or non-spec elements can be added to the EdgeWise database so that these geometries can also be automatically extracted.
  8. Don’t Just Rely on Auto-Extraction: Extraction tolerances can be set in EdgeWise to most efficiently process point clouds to the level of accuracy needed for deliverables. However, sometimes user judgment is called for

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Adam Box

I have been involved in the promotion of new technology to the construction industry for over 15 years. In that time I have seen dramatic changes, not least with the take up of digital capture solutions and their integration into the construction environment. The Verity solution from ClearEdge3D blew me away with its ability to bridge the gap between a captured laser scan and a 3D digital design model. ClearEdge3D is a true leader in construction technology and I am excited about how their technologies will change the industry. Learn more

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